Method of operating a plasma reactor to produce fumed silica and plasma reactor

Abstract

The present invention refers to a method of operating a plasma reactor to produce fumed silica comprising the following method steps: providing a plasma reactor (400, 500, 600, 700, 800) comprising a first heat source with at least two electrodes (101, 102) configured to generate at least one electric arc (117) or a plasma jet (175) by establishing an electric field between the at least two electrodes (101, 102); receiving a feedstock (121) comprising silica, preferably quartz, by a crucible of the plasma reactor (100, 105); preheating the feedstock to generate an electrically conductive melt of the feedstock by providing a second heat source arranged in at least a portion of the crucible and / or arranged outside of the crucible. Further the present invention relates to a plasma reactor for generating an electric arc or a plasma jet for the production of fumed silica the plasma reactor comprising a first heat source, a crucible configured and a second heat source arranged in at least a portion of the crucible and / or arranged outside of the crucible in order to preheat the feedstock in the crucible.

Description

[0001] 202400274 Foreign Filing 1

[0002] METHOD OF OPERATING A PLASMA REACTOR TO PRODUCE FUMED SILICA AND PLASMA REACTOR

[0003] Field of the invention

[0004] The present invention relates to a method of operating a plasma reactor or plasma jet reactor. Further the present invention relates to a plasma reactor for generating an electric arc or a plasma jet for the production of fumed silica, wherein the respective reactor comprises a heat source with at least two electrodes and means to accelerate the initial melting process of the feedstock.

[0005] Background

[0006] Commonly known there are three aggregate states of matter i.e. solid, liquid and gas. It is further known that if the gas phase is further heated a fourth aggregate state can be obtained, which may be called plasma state. Unlike solids, liquids and gases, plasma consists of free electrons and ions-atoms that have lost or gained electrons. The minimum energy required to remove the most loosely electrons, also known as valence electrons, is also called ionization energy and varies from gas to gas. These values are well-known in the art. For example, the molar ionization energy of atomic nitrogen is approximately 1402,3 kJmol / L. and of atomic Argon is approximately 1520,6 kJ mol / L.

[0007] In practice producing ionized gases or plasmas generally requires dissociating molecules of the gas and holding the atoms in an ionized form. A strong heat source producing under others kinetic heat may be used to separate electrons from the atoms. A known technical solution for generating plasma is the application of electric fields, in which sufficient energy is provided for the transformation of gas to plasma such that an ionization of the gas phase can take place. Plasma is an excellent conductor of electricity due to the presence of free-moving ions and electrons.

[0008] The present disclosure relates to a plasma reactor and the operation thereof. Plasma reactors may include at least electrodes which are spaced apart. Typically, a voltage difference is applied to the electrodes and an electric field is established. A gas stream e.g. of inert gas such as nitrogen or Argon or a mixture thereof is introduced to the space between the electrodes. Exposure to the electric filed ionizes the gas and creates a plasma. It is known that plasma reactors can be used for producing high surface silicon dioxide (SiO2). The SiO2 raw products such as quartzite (at least a 80% quartz content) are melted by using as a heat source such as a high temperature electric arc. Due to the thermal plasma process the SiO2 vaporizes. This vapor can be condensed and nucleated quickly to generate ultra-fine powder. The thermal plasma technology using an electric arc to produce electric arc silica or fumed silica, is only rarely used because another production way is used more often as outlaid in the following.

[0009] In the industrial scale for production of fumed silica more often another process, namely the hydrolysis process, is used. The silica (SiO2) produced in this way is called “fumed silica” as well as “pyrogenic” or “flammable” silica because it is produced in a flame. Such fumed silica or pyrogenic silica is industrially formed at high temperature by flame oxidation-hydolysis of silicon halides (SiCk) as disclosed by Degussa in EP 0 015 315.202400274 Foreign Filing 2

[0010] The established industrial hydrolysis converts silicon tetrachloride (SiCk) or other chlorosilanes (e.g. methyltrichlorsilanes, MTCS) in the gas phase and reacts within an oxyhydrogen gas flame above 1000°C to form the desired silicon dioxide. Known commercially available fumed silica produced by this process is AEROSIL® which was formerly produced by Degussa and now by Evonik Industries AG. The ASEROSIL ® fumed silica have primary particles with average diameters between 7 nm and 40 nm, while the specific surface areas are high and range according to BRUNAUER-EMMET-TELLER (BET) between 50 and 380 m2 / g (Technical Information 1411, “AEROSIL ® fumed silica and SIPERNAT® specialty silica in Silane Terminated Polymers (STP)).

[0011] There are numerous target applications for fumed silica such as reinforcing fillers, e.g. for mechanical enhancement of tires, thickening and thixotropic agent, anti-caking for powders and drying agent. Other uses include:

[0012] Adsorbents, antiblocking agents for plastic films, coatings, catalyst supports, matting / grinding or polishing agents, raw material for silica glasses, thermal insulation and additive carriers (See Ullmann’s Encyclopedia of industrial chemistry, Silica Volume 32, section 6.1.7 Uses; pages 483- 485).

[0013] There is the need for alternative processes to produce fumed silica, which do not involve byproducts as HCI and have a high purity. As noted above another but less common way to produce fumed silica is the thermal plasma method, which can be used to decompose crystalline silica such as quartz sand in an electric arc furnace or plasma reactor. One known way is to reduce quartz sand to SiO, wherein as reducing agent coke is used, and to provide at the same time high temperatures. The SiO can subsequently be oxidized. As product electric arc silica is formed. However, it needs to be taken care that the combustion is complete in order to gain fumed silica of high purity. Further, in order to produce high purity silica very pure silica as well as carbon needs to be provided.

[0014] Besides a plasma reactor where a plasma arc or electric arc is created in the center of the reactor, plasma jets reactors can be used. Plasma jets allow an easily controllable process but come with the drawback of a high gas throughput and high gas consumption.

[0015] A shared difficulty or problem for all plasma-arc processes / and plasma jet reactors is the necessity of an electrically conductive material in or near the SiO2. This is needed due to the low electrical conductivity of SiO2. Established solutions for this obstacle are

[0016] 1) Sacrificial electrodes such as graphite, which are consumed / evaporated during the heating process until a stable and electrically conductive melt of SiO2 is generated. In FIG. 2 an example of a sacrificial electrode 112 located in a crucible 111 of a plasma reactor is shown. Further details are described in the detailed description of the Figures. The use of such sacrificial electrodes leads to unwanted formation of SiC and other C-based contaminations of the silica product.

[0017] 2) Addition of additives to generate an electrically conductive material. This is achieved either due to a relatively low melting point of the additives, such as NaOH, or AI2O3 or due to an intrinsic conductivity of the additive e.g. graphite powder. This leads again to a contamination of the silica product with elements of the additive.202400274 Foreign Filing 3

[0018] DE2443130 refers to a plasma arc reactor, using one or more electric arcs for producing silica or aluminum oxides. For initiating the electric arc the electrodes are connected with a piece of carbon, that after application of the electric field heats and is quickly burnt. Such consumable initiators, which are comparable to sacrificial electrodes made of graphite should be avoided due to undesired contaminations, because they lead to carbon-based contamination at least for the initial batch of the produced fumed silica, which should be avoided.

[0019] WO 2022 / 241545 teaches a plasma arc heating process of injected gas such as inert argon gas, to attain a very high temperature plasma. In order to address the problem of low conductivity additives containing AI2O3 are added in the silica to reduce its melting temperature from 1723°C to 1579°C. Any selected additives should have a vapor pressure higher than that of silica under the reactor operating conditions so that the additive does not co-vaporize or decompose with silica to contaminate the fumed silica.

[0020] Accordingly, it is one object of the present invention to avoid contamination of the product i.e the fumed silica. Another important object is to provide a simple and effective process to generate an electrically conductive melt of SiO2 which can subsequently be used in a plasma arc reactor or plasma jet reactor. In particular, it is an object to reduce the time needed for generation of a plasma and in case there was a shutdown to enable a quicker restart of the electric arc or plasma jet. That is to say, there is need to improve an electric arc or jet ignition process.

[0021] Further, it is desirable if one or more new or improved methods for monitoring and / or controlling the operation of plasma reactors for the production of fumed silica is provided.

[0022] Summary of the invention

[0023] It is an object of the present invention to alleviate or address one or more of the above-discussed concerns associated with conventional plasma reactors and corresponding systems and methods, or alleviate or address one or more other concerns or disadvantages. In addition, it is another object to provide one more advantages by comparison with conventional plasma reactors and provide other fumed silica production methods than the flame hydrolysis.

[0024] According to a first aspect a method of operating a plasma reactor is provided in order to produce fumed silica comprising the following method steps:

[0025] providing a plasma reactor configured to provide a first heat source to generate at least one electric arc or a plasma jet by establishing an electric field between at least two electrodes;

[0026] receiving a feedstock comprising silica, preferably quartz, by a crucible of the plasma reactor; preheating the feedstock to generate an electrically conductive melt of the feedstock by providing a second heat source arranged in at least a portion of the crucible and / or arranged outside of the crucible.

[0027] Due to the preheating the feedstock comprising a solid raw material which is preferably crystalline silica and more preferably quartz can be molten more quickly. In this way the time until a start or ignition of the electric arc or plasma jet can be reduced compared to a plasma reactor not having a second heat source for preheating. For plasma reactors with spaced apart electrodes only after the silica is molten the202400274 Foreign Filing 4

[0028] feedstock becomes conductive and between the at least two electrodes an electric field can be applied to establish one electric arc therebetween.

[0029] If a plasma reactor for generating an electric arc or a plasma jet is provided at least two electrodes of opposite polarity, one electrode acting as the cathode and one electrode acting as the anode are part of the electrode arrangement.

[0030] A plurality of electrodes of opposite polarity may also be used in a plasma reactor in order to increase the heat energy. For example, four electrodes can be provided in order to generate two electric arcs. In this way each electrode pair (anode and cathode, respectively) may only supply a fraction of the total power which prolongs the lifetime of the electrodes. Alternatively, two cathodes can generate two electric arcs with one anode arranged below the crucible. In case of a plurality of upper electrodes it is also advantageous to apply the preheating, because as soon as the silica is molten by the preheating step, two or more electric arcs or plasma jets can be ignited at the same time.

[0031] According to another preferred embodiment of the present disclosure the method further comprises the following method steps:

[0032] introducing into the plasma reactor at least one inert gas and / or a reaction gas;

[0033] after the feedstock is molten by said method step of preheating further generating the at least one electric arc or the at least one plasma jet.

[0034] Whilst all gases can be ionized to form a plasma, inert gases are preferred process gases, because no chemical reaction of the fumed target material is being effected. Common process gases are argon (Ar), nitrogen (N2), helium (He), neon (Ne) or mixtures thereof. Argon and nitrogen are the most preferred gases for use because these gases are less cost intensive than e.g. helium. Depending on the selected process gas more or less energy needs to be provided to produce a plasma. As outlaid above for instance the ionization energy of atomic nitrogen is lower (approximately 1402,3 kJmol / L) than the one of Argon (approximately 1520,6 kJ mol / L).

[0035] As noted above the injected inert gas(es) into the reaction chamber are suited to be ionized. Alternatively, or in addition to these process gases reaction gas(es) such as hydrogen may be introduced. Hydrogen can act as reducing gas to decompose vaporized silica to oxidic silica compounds.

[0036] According to another preferred embodiment of the method, the method further comprises:

[0037] after a stable electric arc or plasma jet is generated, silica, preferably quartz, is fed into the reaction chamber of the plasma reactor.

[0038] The plasma reactor may have one or more feed material inlets for introducing silica containing material such as quartz. Advantageously the silica can automatically be added in powder form by a powder feeder. One advantageous or preferred embodiment introduces the powder via a hollow electrode positioned above the crucible, which is configured to receive the silica powder in a respective hollow. By using the preheating operation silica received from the powder feeder can be quickly molten and202400274 Foreign Filing 5

[0039] subsequently fumed silica can be generated free of contaminations and of byproducts or hazardous wastes as encountered in other processes.

[0040] According to another preferred embodiment quenching gas to produce fumed silica is introduced into the plasma reactor.

[0041] By the method step quenching electric arc silica or fumed silica is produced. Whereas the silica exists in the plasma zone in form of vapor, the quenching gas is introduced via a separate gas inlet into the plasma reactor preferably outside of the plasma zone. By the quenching technology the vapor can be cooled and condensed to grow ultra-fine silica powder in the nanoscale. Alternatively, the quenching step can also be performed in the gas outlet.

[0042] According to another example embodiment, the second heat source is an electrical heating system arranged in at least a portion of the crucible or adjacent to the crucible and the electrical heating system is resistive-based and / or inductive-based.

[0043] The inventors have found a new heating system that provides a technical solution to accelerate the lengthy melting process of the feedstock and thereby accelerate the generation of a sufficiently electrically conductive melt. The electrical heating systems is configured to melt the feedstock, preferably silica, into molten silica. By using an electrical heating system, the crucible can be preheated individually and no additives have to be added in the feedstock to improve e.g. the conductivity of the silica or to lower the melting point of the silica additive mixture.

[0044] If the electrical heating system is inductive based induction coils and a respective power source is connected to said inductive coil. The power source such as a frequency generator is connectable to the induction coil and is arranged outside the plasma reactor. Typical frequencies between 250-500 kHz or higher frequencies, preferably between 10-80 kHz, can be applied by the frequency generator.

[0045] Alternatively or additional a further electric resistance heating system may be provided. Both electric heating systems can be heated by electric current, which is applied to both ends of the coil or to resistance wires in the crucible. In case the crucible is formed of an electrically conductive substance such as graphite, no resistance wires are needed and an electric current can be applied through the crucible itself. If a power source causes electric current to flow through the crucible, then the feedstock received in the hollow crucible is preheated and eventually melted. In general, the more input power is provided the more material can be melted in the respective crucible. The power is regulated so that the temperature of the powder, preferably silica, reaches a temperature close or above the melting temperature, which is for silica about 1715 °C. The required power may be up to several 100 kW and depends on the scale of the reactor and the amount of feedstock, preferably quartz powder, received in the crucible.202400274 Foreign Filing 6

[0046] According to another aspect of an embodiment of the present disclosure the second heat source is arranged outside the crucible and is provided as a plasma-torch or a gas torch, which for the method step of preheating is located in the proximity of the feedstock.

[0047] In this way the feedstock, preferably silica, can be preheated directly. The torch can be introduced via a respective inlet port provided in the lid of the housing of the plasma reactor and the tip of the torch is located close to the surface of the silica, which has been received by the crucible. For the gas torch at least one of the following gases can be used: Hydrogen, methane, ethane, acetylene and propene, wherein hydrogen and methane are preferred. The advantage of the use of hydrogen is that this gas source for the plasma torch can also be used as gas source for the reaction gas for the thermal plasma process to form electric arc silica.

[0048] Both kinds of torches have the advantage that they are separate from the crucible and can independently be removed from the plasma reactor. This has the advantage that after the preheating is completed and removal of the respective torch, the gas torch or plasma torch do no more influence the gas streams in the plasma reactor. The above mentioned technical solutions allow an effortless start and restart of an electric arc or plasma jet in the plasma reactor.

[0049] According to another example embodiment, the method further comprises the following method step:

[0050] controlling the state of the feedstock in the crucible by a control unit comprising at least one measurement unit, preferably a camera device or a temperature sensor, configured to determine the molten state of the feedstock and / or an observation window formed in a side wall of the plasma reactor; and

[0051] after determining that an aggregate state of the feedstock is molten via at least one of the measurement unit or the observation window establishing with the first heat source an electric field in order to generate the at least one electric arc or the at least one plasma jet.

[0052] In this way it can be automatically detected and / or by observation of an operator determined if the desired aggregate state has been achieved and an electrical field can be applied between the at least two electrodes to start the first heat source and generate a stable plasma.

[0053] According to a preferred embodiment of the method said generation of the at least one electric arc or the at least one plasma jet is started automatically based on the control unit or manually based on an observation through the observation window;

[0054] wherein optionally after the at least one electric arc or the at least one plasma jet is stable the method step of preheating is deactivated by either turning off the electrical heating system; or removing the second heat source from the plasma reactor.

[0055] After the molten state of the silica has been maintained for a predetermined time period such as a few seconds to preferably maximum 2 minutes the second heat source can be turned off to save energy.202400274 Foreign Filing 7

[0056] According to another aspect of the present disclosure a plasma reactor for generating an electric arc or a plasma jet for the production of fumed silica is provided, wherein said plasma reactor comprises:

[0057] a first heat source comprising at least two electrodes configured to establish at least one electric arc or a plasma jet,

[0058] a crucible configured to receive a feedstock comprising silica, preferably quartz, and;

[0059] a second heat source arranged in at least a portion of the crucible and / or the second heat source is configured to be arranged outside of the crucible in order to preheat the feedstock in the crucible.

[0060] In case the second heat source is separate from the crucible the second heat source can be removed from the plasma reactor after the preheating.

[0061] Accordingly, the inventors have found a new system for a plasma reactor that allows a simple and effective process to generate an electrically conductive melt more quickly. The molten silica can then be used to form high purity fumed silica.

[0062] According to an example embodiment of the plasma reactor the second heat source is an electrical heating system arranged at least in a portion of the crucible or adjacent to the crucible and the electrical heating system is inductive-based and / or resistive-based.

[0063] Using this electrical heating systems allows to heat the crucible and thus indirectly preheat the feedstock received by the crucible. Thus, the crucible is operated as an actively heatable melting pot. Inductive based heating systems can also directly heat the silica. Commonly known electronic components or circuitry commonly used to implement inductive or resistive based heating components can be applied.

[0064] According to a preferred embodiment the electrical heating system comprises an induction coil, which is arranged around the crucible, and / or resistance heating wires.

[0065] For example, an induction coil can be wound around the outer circumference of the crucible, which crucible can be designed as a cylinder with a closed bottom. According to a preferred embodiment the induction coil can concentrically surround the crucible. Other arrangements can be chosen that are either integrated or preferably arranged at an outer portion of the crucible. The induction coil is connected to a power supply. For instance, a medium or high frequency generator may be connected as power supply to the induction coil of the crucible via suited electrodes. Preferably a medium frequency in the range of from 250 Hz to 500 Hz may be applied or high frequencies in the range of 10- 80 Hz.

[0066] Alternatively or additionally, an electrical resistance heating can be provided using either the crucible itself, if the crucible is formed of an electrically conductive material or resistance wires, which may be integrated in the electrically non-conductive body of the crucible. To the crucible or respective conductive portions thereof current can be applied via suited connections such as electrodes.202400274 Foreign Filing 8

[0067] The advantage to preheat the feedstock, preferably quartz, by means of an electromagnetic field or another electrical inductive based heating system is that the field can act on the silica to be heated without combustion gases or other combustibles.

[0068] According to another example embodiment, the second heat source is configured to be arranged outside the crucible and is at least one plasma-torch and / or a gas torch in order to preheat the feedstock.

[0069] In this way the preheating can be done separately via a plasma-torch or gas-torch, respectively. Preferred gases for the gas torch can be selected from the group of the following gases consisting of: Hydrogen, methane, ethane, acetylene, propene or any combination thereof. When a plasma torch is used preferably the same gases can be used as the process gases for the first heat source. Thus, the plasma torch can be connected to the same gas source in connection with a suited valve to regulate the gas flow to the plasma torch. For instance, a respective one-way valve for each supply may be implemented to regulate the gas flow of the plasma torch and to the plasma jet or electric arc, respectively.

[0070] After the preheating is successfully completed to create molten silica, the gas or plasma torch can be removed from the plasma reactor in order not to disturb the gas stream in the reactions chamber. For both the gas torch and plasma torch combustibles such as gases are needed.

[0071] According to a preferred example embodiment the plasma reactor further comprises a control unit comprising a measurement unit, preferably a camera unit or temperature sensor configured to determine the molten state of the feedstock and / or

[0072] an observation window formed in a side wall of the plasma reactor in order to observe if an electrically conductive melt of the feedstock is generated.

[0073] In this way the application of an electrical field between the at least two electrodes can automatically or, after an observation of an operator, manually be started. This improved timing saves energy.

[0074] According to a preferred embodiment, the plasma reactor is configured that after the at least one electric arc or the at least one plasma jet is stable the second heat source is deactivated by

[0075] either turning off the electrical heating system; or

[0076] removing the second heat source from the plasma reactor.

[0077] After the molten state of the silica has been maintained for a predetermined time period such as a few seconds to maximum 2 minutes the second heat source can turned off to save energy.

[0078] According to a preferred embodiment, the plasma reactor comprises a first gas inlet to introduce at least one inert gas and / or a reaction gas; a powder feeder configured to feed silica, preferably quartz, into a reaction chamber of the plasma reactor; and a second gas inlet to introduce quenching gas and to produce fumed silica.202400274 Foreign Filing 9

[0079] Based on the combination of the method step preheating the entire process of producing fumed silica is improved and a high productivity can be realized. Further the energy efficiency can be improved compared to traditional thermal plasma processes not having a second heat source for preheating.

[0080] According to a preferred embodiment the crucible is made of a material having a higher melting point than the feedstock and is selected from the group of materials consisting of:

[0081] graphite, tungsten, corundum, magnesite, silicon carbide or other fire-resistant materials or combinations thereof.

[0082] The material of the crucible is further required to have enough heat resistance to stand high temperatures over 1750°, preferably more than 2000 °C, more preferably more than 2500 °C. If the material is an electrically conductive substance such as graphite then a power source can contact the crucible via electrodes and cause electric current to flow through the crucible for resistive-based preheating. The current can be regulated to reach at least the melting temperature of the silica.

[0083] Ultrafine silica powder in the nanoscale with excellent purity and high surface with a BRUNAUER-EMMET and TELLER (BET) surface of at least 15 m2 / g, preferably at least 30 m2 / g, is obtained by means of the above mentioned process, wherein the feedstock is molten by said method step of preheating to generate a stable electric arc or the at least one plasma jet. Further said production process comprises the steps introducing into the plasma reactor at least one inert gas and / or a reaction gas and optionally the method step quenching can be performed.

[0084] Additionally, a method is provided wherein a traditional plasma reactor can be upgraded with a second heat source. This can be done by providing a crucible with an electrical heating system such as an induction coil and power supply electrodes as well a power source. If the crucible is made of an electrically conductive material electrodes and a suited power source can be connected to the crucible in order to preheat the crucible. Alternatively, the electric arc plasma reactor or plasma jet reactor can be upgraded by providing in the lid of the housing another port in order to introduce therethrough a torch for preheating the feedstock in the crucible.

[0085] Brief Description of the Figures

[0086] The accompanying figures illustrate exemplary embodiments of the disclosure and serve to explain, by way of example the principles of the disclosure and are not intended to be drawn to scale or to restrict the disclosure to the embodiment illustrated in the figures. Where technical features in the figures or detailed description are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures and description. For purposes of clarity, not every component may be labelled in every figure.

[0087] As used herein, the terms “top,” “bottom,” “upper,” “lower,” and “above” are used to provide a relative relationship between structures. The use of these terms does not indicate or require that a particular structure must be located at a particular location in the apparatus or plasma reactor or a respective202400274 Foreign Filing 10

[0088] system. That is to say the main axis of a plasma reactor is usually vertical, however, inlcined plasma reactors are also encompassed. Some drawings may indicate the components using block diagrams and may not represent the internal circuitry of each component. It will be appreciated by those skilled in the art that disclosure of such drawings includes the invention of electrical components, electronic components, or circuitry commonly used to implement such components.

[0089] FIG. 1 shows plasma reactor for electric arc generation according to the prior art using an additive in the feedstock;

[0090] FIG. 2 shows another prior art plasma reactor using a sacrificial electrode;

[0091] FIG. 3 shows another prior art plasma using as first heat source a plasma jet;

[0092] FIG. 4 shows an exemplary embodiment of a plasma reactor of the present invention with a second heat source comprising an inductive based electric heating system;

[0093] FIG. 5 shows another exemplary embodiment of a plasma reactor with a second heat source comprising a resistive based electric heating system;

[0094] FIG. 6 shows an embodiment of a plasma jet reactor with a second heat source comprising a resistive based electric heating system;

[0095] FIG. 7 shows another exemplary embodiment of a plasma reactor with a second heat source comprising a plasma torch;

[0096] FIG. 8 shows another exemplary embodiment of a plasma reactor with a second heat source comprising a gas torch; and

[0097] FIG. 9 shows a flow chart of an exemplary embodiment of a method for operation of a plasma reactor with two heat sources.

[0098] Detailed description

[0099] FIG. 1 shows an example of a plasma reactor 100 for producing an electric arc or plasma arc. FIG. 1 shows an example of a plasma reactor 100 according to the prior art comprising two electrodes 101 , 102 that are spaced apart in the vertical direction. The plasma reactor 100 comprises a housing 115 with a lower housing 113 and an upper housing lid 114 including a reactor chamber 110 and an insulation 118. There is an electric field generator 170 to apply an electric field between the electrodes 101 and 102. The feedstock 121 in the crucible 111 comprises additives 127 (shown schematically as black circles) in order to lower the melting point of the feedstock 121, which is in the unmolten state preferably crystalline silica. Silica powder 122 can be fed by a powder feeder 120 via a dosing system 125. Once the feedstock 121 in the crucible 111 is in a molten state, an electric arc 117 can be formed. The produced silica in the form of ultrafine particles leaves the plasma reactor with the gas stream through the gas outlet 134 and can be collected in a common way such as a filter unit.202400274 Foreign Filing 11

[0100] FIG. 2 shows another prior art plasma reactor 200 configured to generate an electric arc 117. The general design is similar to the plasma reactor 100 of FIG. 1 , except that the upper electrode is not used as a feed inlet and that there is a sacrificial electrode 112 placed between the electrodes 101 and 102. The graphite sacrificial electrode 112 is used to conduct electricity and thereby facilitates the melting of the feedstock as commonly known. In this way the ignition of the plasma reactor 200 can be accelerated in a conventional manner. The electrode 112 is referred to as sacrificial because until a stable and electrically conductive melt of SiO2 is generated, the electrode 112 will be consumed. The use of such sacrificial electrode 112 has the disadvantage that its consumption and vaporization leads to unwanted formation of SiC and other C-based contaminations of the silica product.

[0101] The sacrificial graphitic electrode 112 is arranged in the middle of the graphite crucible 111 and has contact to the crucible bottom, which is located above the electrode 101 (e.g. a metal anode). The crucible 111 is preferably filled with quartz as feedstock 121 outside of the plasma reactor 200 and then inserted into the plasma reactor 200 on the first electrode 101. Alternatively, the first filling of the crucible 111 can be done by other suited means. The sacrificial electrode 112 can produce an electric field in close proximity to the field produced by the tip of the upper electrode 102. The use of such sacrificial electrode 112, optionally in combination with a movable upper electrode 102, addresses the problem of the high resistivity of silica at low temperatures and may ease the start of the arc transfer.

[0102] The plasma reactor 200 of FIG. 2 further shows schematically gas sources 141 , 142 and 143. In order to produce electric arc silica 124 the reaction chamber 110 is flushed with inert gases as Argon (Ar, 141) and nitrogen (N2, 142) and the reaction gas 143, which is the reducing agent H2. To start the electric arc 117, plasma generating power is applied to the electrodes 101 , 102 by the electric field generator 170.

[0103] The plasma reactor 200 is equipped with a further gas inlet 132, which is used as quenching port for quenching gas 144 such as water steam (H2O). It is noted that the gas inlet 132 has a one-way dosing valve 145 and a heating 135, to heat the steam above 110°C in order to avoid condensation of the water steam 144 before entering the reactor chamber 110.

[0104] An alternative position (not shown) of the gas inlet 132 is in the gas outlet 134. At this higher position the injection of the quenching gas 144 does not disturb the streams in the reaction chamber 110.

[0105] The plasma reactor of FIG. 2 further shows downstream of the gas outlet 134 a filter unit 130 which separates particles of the electric arc silica 124 from the offgas 146 using a filter 147 (indicated with a dashed line). Other known separation units may be used as cyclones.

[0106] The high conductivity of a sacrificial electrode 112 made of graphite ensures that a large amount of energy is transferred to the silica in the feedstock 121 , resulting in faster and more efficient melting. However, in order to avoid the presence of the sacrificial electrode and associated contamination an alternative way of accelerating the melting process and thereby initiating the electric arc needs to be found.202400274 Foreign Filing 12

[0107] Another well-known technology to use electricity between electrodes to create a plasma zone is schematically shown in FIG. 3. FIG. 3 shows an illustration of a prior art plasma jet reactor 300, with a housing 115 having a lower housing 113 to receive a crucible 111 with a feedstock 121 comprising silica. A plasma arc 175 is created in the center of the plasma reactor 300. Both electrodes are located in the top of the plasma jet reactor and each of the electrode (anode / cathode) are electrically connected via respective lines 171 and 172 with the negative and positive pole of the electric field generator 170. The two electrodes i.e. anode and cathode are arranged in the top of the plasma reactor 300 and are spaced apart from each other to create an electric arc therebetween.

[0108] By introducing gas between the electrodes the traditional plasma jet reactor can create a directional flow of plasma, which can heat and subsequently melt the feedstock 121 in the crucible 111. This method is easily controllable but has the disadvantage that a high gas throughput and high gas consumption is required. After the plasma jet 175 is generated, silica powder 122 can be added via the dosing system 125 of the powder feeder 120 and vaporized in the plasma jet 175 to form at least partially oxidic silica compounds. The gas stream leaving the plasma jet reactor 300 via the gas outlet 134 carries the reaction products away from the plasma zone and after condensation and cooling provides fumed silica as output products of the plasma jet reactor 300. The fumed silica produced is amorphous and can be separated off in a common manner as for example with a filter unit as illustrated in FIG. 2.

[0109] Embodiments according to the present invention will now be described, by way of example, with reference to the drawings FIG. 4 to FIG. 9.

[0110] FIG. 4 shows an exemplary embodiment of a plasma reactor 400 with a second heat source comprising an inductive based electric heating system 211. The FIG. 4 shows a cross section of the crucible 11 which has a hollow to receive the feedstock 121. Alternatively, the crucible 111 can be of a cylindrical shape with a closed bottom or being having partially a cylindrical upper portion and in the lower portion a hemispherical shape. The electrical heating system 211 can be an induction coil wound around the crucible 111. Said inductive coil can be coupled to the crucible 111. The inductive heating system 211 is connected with common electrical components such as wires to a respective power source (not shown). In this way for example a two-terminal inductive heating system 211 can be formed that stores energy in a magnetic field when an electric current flows through it and produces heat to preheat the feedstock comprising silica in the crucible 111. Commonly known electronic components or circuitry commonly used to implement inductive based heating components can be applied. For example, a power supply system (not shown) such as a medium-frequency generator connectable to the induction coil may be arranged outside the plasma reactor. Preferred medium frequencies which are to be applied to the induction coil range between 250 - 500 Hz. Alternatively high frequencies may be preferably in a range between 10-80 kHz. In this way the feedstock 121 can be individually preheated and the ignition process can be shortened compared to a traditional crucible 111 with no electrical heating.

[0111] After a stable electric arc is generated as indicated by reference sign 117, the second heat source i.e. the inductive based electric heating system 211 can be turned off.202400274 Foreign Filing 13

[0112] For the generation of the electric arc process an introduction of gases as argon or nitrogen or a mixture thereof into the reaction chamber 110 is required. Furthermore, a quenching gas (not shown in FIG. 4) can be introduced in the gas outlet 134 to produce fumed silica. For the introduction of gas common gas inlets for example shown in FIG: 2 (see reference signs 131 und 132 in FIG. 2) can be used for this purpose.

[0113] An advantage of the use of a second heat source for preheating is that the time needed for generation of a plasma can be significantly reduced and in case there was a shutdown a quicker restart of the electric arc or plasma jet is possible. That is to say, by using as second heat source an electrical heating system (see reference sign 211) the electric arc or plasma jet ignition process can be improved.

[0114] In the following exemplary method steps are described how to produce electric arc silica with an electric arc plasma generator in accordance with the present invention.

[0115] For all inventive examples a laboratory scale plasma reactor such as shown in FIG. 4, 5, 7 and 8 with an electric arc 117 can be used. The inventors found that the following conditions can be selected for a production of high surface electric arc silica.

[0116] A plasma reactor 400, 500, 700 or 800 as shown in FIG. 4, 5,7 or 8 having all components as gas inlets 131 and 132 in analogy with FIG. 2 except that there is no sacrificial electrode arranged in the crucible. The inventive plasma reactors differ further from the prior art reactors that a second heat source such as an electrical heating system 211 , 212 in or at the crucible 111 is provided. Alternatively, a separate second heat source in form of a plasma torch 201 or a gas torch 202 can be provided. As initial method step (see also reference sign 905 in method 900 as shown in FIG. 9 below) 60g of fine sized quartz (<0.8 mm) is placed in the crucible 111 to form the initial feedstock 121 in the plasma reactor 400, 500, 700, 800.

[0117] Then the preheating with the second heat source 211 , 212 or 201 / 202 is initiated. After it has been observed that the feedstock 121 is molten, the plasma process gas is injected into the reaction chamber 110 for initiation of thermal plasma process. In particular, the reactor is flushed with an Argon (Ar) volume flow rate of 3 L / min.

[0118] The following electric field conditions are chosen:

[0119] a power of about 6 kW with an average current of 100A is applied to the two electrodes 101 , 102. Once the transferred arc is stable, the second heat source 211 , 212, 201 or 202 can be turned off or removed, respectively. Then optionally 1 L / min of the reaction gas hydrogen (H2) is added to the system and after 2 min (for ensuring a liquid silica melt) fine sized quartz powder is added through the hollow cathode 102 with a feed rate of 400 g / h. Further optionally, an additive can be added to the silica powder 122 in order to improve the surface properties of the produced fumed silica such as an increased the silanol density. One optional additive for promoting isolated hydroxyl groups on the surface of the silica is a chloride salt, which may be added in an amount of 10 w% or less, preferably equal or less than 4 w / %. Preferred chloride salts for the purpose to increase the viscosity may be sodium chloride or ammonium chloride. After a stable operation of the electric arc 117, optionally a quenching gas mixture of water steam and nitrogen is introduced into the reaction chamber 110, wherein water vapor (H2O) is injected with a volume202400274 Foreign Filing 14

[0120] flow of 50 L / h mixed with a volume flow of nitrogen (N2) of 60 L / h. In this way high surface electric silica produced.

[0121] The plasma reactor as shown in the Figures and described for the above exemplary production process of electric arc silica is of laboratory scale. However, it is believed that the results are also representative for the production of electric arc silica with high surface and optionally with desired silanol densities in plasma reactors of larger scales. Furthermore, such laboratory scale reactors can also be upscaled in order industrially produce electric arc silica. If the plasma reactor is scaled up for higher production rates, then not only the size of the reactor but also the generating power may be increased from several tens of kW up to several MW. In general, increasing the arc power will enhance the silica vaporization rate. The increasingly stringent requirements for high purity fumed silica and the need for hazardous or waste free processes makes the novel and inventive method an attractive alternative to conventional industrial technologies as the flame hydrolysis having as byproduct HCI. One further advantage is that the plasma reactor according to the present invention can be restarted more quickly after being switched off. Using the methods according to the above are examples of efficient and reliable production processes of electric arc silica with the desired properties such as BRUNAUER, EMETT und TELLER (BET) surface of at least 15 m2 / g and more preferably at least 30 m2 / g.

[0122] FIG. 5 shows another exemplary embodiment of a plasma reactor 500 with a second heat source in the crucible 111. The crucible 111 shows a resistive based heating system 212 which optionally may use, which are schematically indicated with white dots. Any further electronic component or circuitry commonly used to implement such a resistive based heating system 212 as a power source (see as example reference sign 180 in FIG. 6) is not shown. Further it has to be noted that in case the material of the crucible 111 is electrically conductive such as graphite then there is no need of integrating wires into the crucible and an external power source can be connected directly to the crucible in order to initiate the resistance heating via an electrical current.

[0123] FIG. 6 shows the same resistive based heating system 212 as in FIG. 5 but in combination with a plasma jet reactor 600. The plasma jet has only upper electrodes 101 and 102 which are spaced apart and electrically connected to the plasma generating power source 170 via lines 171 and 172. The crucible 111 has either integrated resistive wires or is itself electrically conductive. The crucible 111 is connected to another power source 180 in order to apply current via the respective lines 181 and 182. In this way the feedstock in the form of crystalline silica can be preheated and eventually molten via the crucible 111. This embodiment shown in FIG. 6 provides the second heat source i.e. the resistive based electrical heating system 212 by at least portions of the crucible 111. Optionally, an induction coil (not shown) can be provided in addition.

[0124] FIG. 7 shows another exemplary embodiment of a plasma reactor 700 with a second heat source comprising a plasma torch 201. The principle of the plasma torch 201 is similar to a plasma jet, wherein the torch 201 has two electrodes and after application of an electrical field and injection of gas a plasma torch can be established. It is an advantage that, after the plasma torch 201 is used for efficiently preheating and melt the silica, the plasma torch 201 can be removed from the reaction chamber 110 and does not disturb the gas flow in the reaction chamber 110.202400274 Foreign Filing 15

[0125] FIG. 8 shows another exemplary embodiment of a plasma reactor 800 with a second heat source comprising a gas torch 202. A gas torch 202 needs less energy than a plasma torch and can targeted preheat the silica in the crucible until it is molten. The gases that can be used for the gas torch can be selected from the following group: Hydrogen, methane, ethane, acetylene and propene, wherein hydrogen and methane are preferred.

[0126] FIG. 9 shows a flowchart of an exemplary embodiment of a method for operating a plasma reactor or a plasma jet reactor. It should be noted that method 900 may be performed differently than depicted. For example, an additional operation or method step may be performed and / or a depicted operation may not be performed, and / or some of the depicted operations may be performed in a different order.

[0127] As first method step 901 a plasma reactor or a plasma jet reactor is provided. In some embodiments, the operations of the method 900 may be performed by a plasma reactor 400, 500, 700, 800 or a plasma jet reactor 600 having a single pair of electrodes (101, 102). Alternatively, more than one upper electrode or pair of electrodes may be provided.

[0128] The method step 905 referring to receiving a feedstock in a crucible 111 of the respective reactor is required before the feedstock 121, preferably comprising silica, can be preheated in the subsequent method step 910.

[0129] There are alternative and / or combinable options how to preheat the feedstock. On the one hand at block 915, the preheating operation is performed electrically, wherein the second heat source is integrated or coupled to the crucible 111. As indicated in the flow chart the heating system is either inductive based (see method step 911 or 211) or resistive based (912, 212). A combination of both electrical heating system is also possible as shown schematically in step 911.

[0130] On the other hand the second heat source may be provided separate from the crucible 111, wherein the second heat source can be a gas torch 913 and / or a plasma torch 914.

[0131] By using one or more of the above mentioned embodiments of a second heat source the method step melting 920 is performed. In this way the feedstock changes its state and a conductive material such as a silica melt is obtained.

[0132] After the silica in the crucible is molten in the following step 930 an electric arc (if a plasma reactor is provided in step 901) or a plasma jet (if a plasma jet reactor is provided in step 901) can be generated. For step 930 other operations such as introducing at least one inert gas and / or reaction gas into the respective reactor is required.

[0133] Further steps (not shown) can optionally follow in order to produce electric silica in the respective reactors. These may comprise to further introduce a reaction gas and a quenching gas. The quenching gas is directed downstream of the respective plasma zone in order to form fine sized electric silica. As202400274 Foreign Filing 16

[0134] last operation a separation is required which use common filter systems or other suited operation as cyclones.

[0135] Applying one or more of the preheating method steps (911-915) can significantly improve the efficiency of ignition and shorten the ignition process of an electric arc or plasma jet, respectively. In case there was a shutdown a quicker restart of the electric arc or plasma jet is possible. That is to say, by using as second heat source either an electrical heating system 211 , 212 or a separate torch 201 , 202 the electric arc or jet ignition process can be improved.

[0136] In this way no sacrificial electrode needs to be inserted into the furnace and it can be avoided that a sacrificial electrode comes into contact with the silica being melted. Such sacrificial electrodes are known to contaminate the latter when consumed for the start of the respective plasma zone. Such contamination can be avoided. When using as a plasma torch then the same process gas as for the generation of the plasma jet or the electric arc can be used. Thus, the mentioned heating method does not introduce contamination. The same applies for electrical heating systems for preheating.

[0137] The present invention is also characterized by the following items:

[0138] 1. Method of operating a plasma reactor to produce fumed silica comprising the following method steps:

[0139] providing (901) a plasma reactor (400, 500, 600, 700, 800) comprising a first heat source with at least two electrodes (101 , 102) configured to generate at least one electric arc (117) or a plasma jet (175) by establishing an electric field between the at least two electrodes (101, 102);

[0140] receiving (905) a feedstock (121) comprising silica, preferably quartz, by a crucible of the plasma reactor (100, 105);

[0141] preheating (910) the feedstock to generate (920) an electrically conductive melt of the feedstock by providing a second heat source arranged in at least a portion of the crucible (111) and / or arranged outside of the crucible (111).

[0142] 2. Method according to item 1 , the method further comprising the following method steps:

[0143] introducing into the plasma reactor (400, 500, 600, 700, 800) at least one inert gas and / or a reaction gas;

[0144] after the feedstock (121) is molten by said method step of preheating further generating the at least one electric arc (117) or the at least one plasma jet (175).

[0145] 3. Method according to item 2, the method further comprising:

[0146] after a stable electric arc (117) or plasma jet (175) is generated feeding silica (122), preferably quartz, into the reaction chamber (110);

[0147] optionally introducing quenching gas (144) to produce fumed silica.202400274 Foreign Filing 17

[0148] 4. Method according to any of the items 1 to 3, wherein the second heat source is an electrical heating system arranged in at least a portion of the crucible (111) or adjacent to the crucible (111) and the electrical heating system is resistive-based (212) and / or inductive-based (211).

[0149] 5. Method according to any of the items 1 to 3; wherein the second heat source arranged outside the crucible is a plasma-torch (201) or a gas torch (202), which for the method step of preheating is located in the proximity of the feedstock (121).

[0150] 6. Method according to any of the preceding items; further comprising:

[0151] controlling the state of the feedstock in the crucible by a control unit comprising at least one measurement unit, preferably a camera device or a temperature sensor, configured to determine the molten state of the feedstock and / or an observation window formed in a side wall of the plasma reactor (400, 500, 600, 700, 800); and

[0152] after determining that an aggregate state of the feedstock (121) is molten via at least one of the measurement unit or the observation window establishing with the first heat source an electric field in order to generate the at least one electric arc (117) or the at least one plasma jet (175).

[0153] 7. Method according to item 6 ;

[0154] wherein said generation of the at least one electric arc (117) or the at least one plasma jet (175) is started automatically based on the control unit or manually based on an observation through the observation window;

[0155] wherein optionally after the at least one electric arc (117) or the at least one plasma jet (175) is stable the method step of preheating is deactivated by

[0156] either turning off the electrical heating system (211, 212); or

[0157] removing the second heat source, preferably a plasma torch (201) or a gas torch (202), from the plasma reactor.

[0158] 8. Plasma reactor for generating an electric arc or a plasma jet for the production of fumed silica the plasma reactor comprising:

[0159] a first heat source comprising at least two electrodes (101 , 102) configured to establish at least one electric arc (117) or a plasma jet (175),

[0160] a crucible (111) configured to receive a feedstock comprising silica, preferably quartz, and;

[0161] a second heat source arranged in at least a portion of the crucible (111) and / or configured to be arranged outside of the crucible (111) in order to preheat the feedstock (121) in the crucible (111).

[0162] 9. The plasma reactor of item 8, wherein the second heat source is an electrical heating system arranged at least in a portion of the crucible or adjacent to the crucible and the electrical heating system is inductive-based (211) and / or resistive-based (212).

[0163] 10. The plasma reactor of item 9, wherein the electrical heating system comprises an induction coil, which is arranged around the crucible (111), and / or resistance heating wires.202400274 Foreign Filing 18

[0164] 11. The plasma reactor of item 8, wherein the second heat source is configured to be arranged outside the crucible and comprises at least one plasma-torch (201) and / or a gas torch (202) in order to preheat the feedstock.

[0165] 12. The plasma reactor of any of the preceding items, further comprising a control unit comprising a measurement unit, preferably a camera unit or temperature sensor configured to determine the molten state of the feedstock (121) and / or

[0166] an observation window formed in a side wall of the plasma reactor (400, 500, 600, 700, 800) in order to observe if an electrically conductive melt of the feedstock (121) is generated.

[0167] 13. The plasma reactor of item 12, wherein based on the determination of the control unit and / or an observation the generation of the at least one electric arc (117) or plasma jet (175) is started automatically or by an operator.

[0168] 14. The plasma reactor according to any of the preceding items,

[0169] wherein the plasma reactor (400, 500, 600, 700, 800) is configured to produce fumed silica further comprising:

[0170] a first gas inlet (131) to introduce at least one inert gas (141, 142) and / or a reaction gas (143); a powder feeder (120) configured to feed silica (122), preferably quartz, into a reaction chamber of the plasma reactor (400, 500, 600, 700, 800); and

[0171] a second gas inlet to introduce quenching gas (144) and to produce fumed silica (124).

[0172] 15. The plasma reactor of any of the preceding items wherein the crucible (111) is made of a material having a higher melting point than the feedstock and is selected from the group of materials consisting of:

[0173] graphite, tungsten, corundum, magnesite, silicon carbide, other fire-resistant materials or combinations thereof materials or combinations thereof.

[0174] Reference list

[0175] 100 plasma reactor with hollow top electrode for silica feed

[0176] 101 first electrode

[0177] 102 second electrode

[0178] 110 reactor chamber

[0179] 111 crucible

[0180] 112 sacrificial electrode

[0181] 113 lower housing with bottom and sidewalls

[0182] 114 upper housing lid

[0183] 115 housing

[0184] 116 bottom of lower housing

[0185] 117 electric arc

[0186] 118 insulation of reactor202400274 Foreign Filing 19

[0187] 120 powder feeder

[0188] 121 feedstock in crucible in molten state

[0189] 122 silica powder

[0190] 124 product: electric arc silica

[0191] 125 dosing system

[0192] 127 additive in the feedstock

[0193] 130 filter unit

[0194] 131 first gas inlet

[0195] 132 second gas inlet

[0196] 134 gas outlet

[0197] 135 heating of gas inlet

[0198] 141 first inert gas

[0199] 142 second inert gas

[0200] 143 reducing agent

[0201] 144 quenching gas

[0202] 145 dosing valves

[0203] 146 off gas

[0204] 147 filter

[0205] 170 electric field generator or power source for generating a plasma 171 electric line

[0206] 172 electric line

[0207] 175 plasma jet

[0208] 180 power source

[0209] 181 electric line

[0210] 182 electric line

[0211] 200 plasma reactor with sacrificial electrode in the crucible

[0212] 201 plasma torch

[0213] 202 gas torch

[0214] 211 inductive based heating system

[0215] 212 resistive based heating system

[0216] 300 plasma jet reactor

[0217] 400 electric arc plasma reactor with an inductive based heating system 500 electric arc plasma reactor with a resistive based heating system 600 plasma jet reactor with a resistive based heating system

[0218] 700 electric arc plasma reactor with a plasma torch

[0219] 800 electric arc plasma reactor with a gas torch

[0220] 900 method according to an embodiment of the present disclosure 901 first method setp

[0221] 905 second method step202400274 Foreign Filing 20 910 method step of preheating

[0222] 915 method step directed to electrical heating 911 inductive based heating

[0223] 912 resistive based heating

[0224] 913 heating with gas torch

[0225] 914 heating with plasma torch

[0226] 920 method step of melting

[0227] 930 generating an electric arc or plasma jet

Claims

202400274 Foreign Filing 21CLAIMS1. Method of operating a plasma reactor to produce fumed silica comprising the following method steps:providing (901) a plasma reactor (400, 500, 600, 700, 800) comprising a first heat source with at least two electrodes (101 , 102) configured to generate at least one electric arc (117) or a plasma jet (175) by establishing an electric field between the at least two electrodes (101 , 102); receiving (905) a feedstock (121) comprising silica, preferably quartz, by a crucible of the plasma reactor (100, 105);preheating (910) the feedstock to generate (920) an electrically conductive melt of the feedstock by providing a second heat source arranged in at least a portion of the crucible (111) and / or arranged outside of the crucible (111).

2. Method according to claim 1 , the method further comprising the following method steps:introducing into the plasma reactor (400, 500, 600, 700, 800) at least one inert gas and / or a reaction gas;after the feedstock (121) is molten by said method step of preheating further generating the at least one electric arc (117) or the at least one plasma jet (175).

3. Method according to claim 2, the method further comprising:after a stable electric arc (117) or plasma jet (175) is generated feeding silica (122), preferably quartz, into the reaction chamber (110);optionally introducing quenching gas (144) to produce fumed silica.

4. Method according to any of the claims 1 to 3, wherein the second heat source is an electrical heating system arranged in at least a portion of the crucible (111) or adjacent to the crucible (111) and the electrical heating system is resistive-based (212) and / or inductive-based (211).

5. Method according to any of the claims 1 to 3, wherein the second heat source arranged outside the crucible is a plasma-torch (201) or a gas torch (202), which for the method step of preheating is located in the proximity of the feedstock (121).

6. Method according to any of the preceding claims, further comprising:controlling the state of the feedstock in the crucible by a control unit comprising at least one measurement unit, preferably a camera device or a temperature sensor, configured to determine the molten state of the feedstock and / or an observation window formed in a side wall of the plasma reactor (400, 500, 600, 700, 800); andafter determining that an aggregate state of the feedstock (121) is molten via at least one of the measurement unit or the observation window establishing with the first heat source an electric field in order to generate the at least one electric arc (117) or the at least one plasma jet (175).202400274 Foreign Filing 227. Method according to claim 6,wherein said generation of the at least one electric arc (117) or the at least one plasma jet (175) is started automatically based on the control unit or manually based on an observation through the observation window;wherein optionally after the at least one electric arc (117) or the at least one plasma jet (175) is stable the method step of preheating is deactivated byeither turning off the electrical heating system (211 , 212); orremoving the second heat source, preferably a plasma torch (201) or a gas torch (202), from the plasma reactor.

8. Plasma reactor for generating an electric arc or a plasma jet for the production of fumed silica the plasma reactor comprising:a first heat source comprising at least two electrodes (101 , 102) configured to establish at least one electric arc (117) or a plasma jet (175),a crucible (111) configured to receive a feedstock comprising silica, preferably quartz; and a second heat source arranged in at least a portion of the crucible (111) and / or configured to be arranged outside of the crucible (111) in order to preheat the feedstock (121) in the crucible (111) and if arranged outside of the crucible to be removed after the preheating.

9. The plasma reactor of claim 8, wherein the second heat source is an electrical heating system arranged at least in a portion of the crucible or adjacent to the crucible and the electrical heating system is inductive-based (211) and / or resistive-based (212).

10. The plasma reactor of claim 9, wherein the electrical heating system comprises an induction coil, which is arranged around the crucible (111), and / or resistance heating wires.

11. The plasma reactor of claim 8, wherein the second heat source is configured to be arranged outside the crucible and comprises at least one plasma-torch (201) and / or a gas torch (202) in order to preheat the feedstock.

12. The plasma reactor of any of the claims 8 to 11 , further comprising a control unit comprising a measurement unit, preferably a camera unit or temperature sensor configured to determine the molten state of the feedstock (121) and / oran observation window formed in a side wall of the plasma reactor (400, 500, 600, 700, 800) in order to observe if an electrically conductive melt of the feedstock (121) is generated.

13. The plasma reactor of claim 12, wherein based on the determination of the control unit and / or an observation the generation of the at least one electric arc (117) or plasma jet (175) is started automatically or by an operator.

14. The plasma reactor according to any of the claims 8 to 13,wherein the plasma reactor (400, 500, 600, 700, 800) is configured to produce fumed silica202400274 Foreign Filing 23further comprising:a first gas inlet (131) to introduce at least one inert gas (141, 142) and / or a reaction gas (143); a powder feeder (120) configured to feed silica (122), preferably quartz, into a reaction chamber of the plasma reactor (400, 500, 600, 700, 800); and;a second gas inlet to introduce quenching gas (144) and to produce fumed silica (124).

15. The plasma reactor of any of the claims 8 to 14 wherein the crucible (111) is made of a material having a higher melting point than the feedstock and is selected from the group of materials consisting of:graphite, tungsten, corundum, magnesite, silicon carbide, other fire-resistant materials or combinations thereof materials or combinations thereof.

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